The invention relates to polymeric or polymerizable formaldehyde-free containing materials for imparting sag resistance in panels, for example, fibrous panels and acoustical panels, such as ceiling tiles.
Acoustical panels (or tiles) are specially designed systems that are intended to improve acoustics by absorbing sound and/or reducing sound transmission in an indoor space, such as a room, hallway, conference hall, or the like. Although there are numerous types of acoustical panels, a common variety of acoustical panel is generally composed of mineral wool fibers, fillers, colorants and a binder, as disclosed, for example, in U.S. Pat. No. 1,769,519. These materials, in addition to a variety of others, can be employed to provide acoustical panels with desirable acoustical properties and other properties, such as color and appearance.
In order to prepare panels, a selected combination of fibers, fillers, bulking agents, binders, water, surfactants and other additives is combined to form a slurry and processed. Cellulosic fibers are typically in the form of recycled newsprint. The bulking agent is typically expanded perlite. Fillers may include clay, calcium carbonate or calcium sulfate. Binders may include starch, latex and reconstituted paper products linked together to create a binding system that facilitates locking all ingredients into a desired structural matrix.
Organic binders, such as starch, are often the primary component providing structural adhesion for the panel. Starch is a preferred organic binder because, among other reasons, it is relatively inexpensive. For example, panels containing newsprint, mineral wool and perlite can be bound together economically with the aid of starch. Starch imparts both strength and durability to the panel structure, but is susceptible to problems caused by moisture. Moisture can cause the panel to soften and sag, which is unsightly in a ceiling and can lead to the weakening of the panel.
One method used to counter problems caused by moisture in panels is to back-coat the panels with a melamine-formaldehyde resin based coating with or without a urea-formaldehyde component. When such a formaldehyde resin based coating is exposed to moisture or humidity it tends to resist the compressive forces on the back surface that result from the downward sagging movement.
Cured melamine-formaldehyde resins have a rigid and brittle crosslinked structure when properly cured. This rigid structure acts to resist the compressive forces on the back surface that result from the downward sagging movement. However, formaldehyde resins tend to emit formaldehyde, which is a known environmental irritant.
To decrease formaldehyde emissions, formaldehyde reactive materials, such as urea, have been added to scavenge the free formaldehyde. Unfortunately, such small molecule scavengers end cap the reactive groups of the formaldehyde resin, preventing significant levels of cross-linking from occurring. As a result, the characteristic highly cross-linked polymer structure is never formed. The resulting coating is weak and will not act to resist sag.
Although there are a variety of commercially available acoustical panel products classified as low volatile organic chemical (VOC) emitters, these products emit detectable levels of formaldehyde due to the presence of various formaldehyde emitting components that are employed in these panels. Although formaldehyde emissions that are generated during heat exposure in the manufacturing process may be exhausted into stacks or thermal oxidizers, the resulting product will still contain residual formaldehyde, which is emitted upon installation. A reduction in formaldehyde emissions, or elimination of such emissions, will provide improved indoor air quality in those locations where acoustical panels are installed, such as public buildings including schools, healthcare facilities, or office buildings.
What is needed is a coating capable of counteracting the moisture susceptibility of the panels without emitting an environmental irritant.